Process for producing polyphenylene ether

ABSTRACT

At the time of preparing polyphenylene ether resin, there can be separated and recovered efficiently an aromatic compound solvent, amines making an azeotrope with water (hereafter, referred to as ‘the amines’ for short.) and methanol. 
     A method for producing polyphenylene ether, which comprises 
     (a) a step for synthesizing polyphenylene ether by subjecting phenol to oxidative polymerization in the presence of a copper compound and amines in an aromatic compound solvent, 
     (b) a step for precipitating polyphenylene ether particles by adding methanol into the solution of polyphenylene ether in the aromatic compound solvent obtained by the step (a), 
     (c) a step for solid-liquid separating a slurry of polyphenylene ether obtained by the step (b), and then washing the separated polyphenylene ether particles with methanol to obtain the polyphenylene ether, 
     (d) a step for adding water to a filtrate obtained by the step (c) to mix them, and then liquid-liquid separating the mixture into a phase consisting mainly of the aromatic compound and a phase consisting mainly of methanol and water, and 
     (e) a step for supplying the phase consisting mainly of methanol and water, obtained at the step (d) to the middle portion of a distilled column to perform distillation, and separating out a distillate liquid consisting mainly of methanol, a bottom liquid consisting mainly of water and a side-cut liquid containing the amines by distillation, recycling the distillate liquid consisting mainly of methanol as methanol of the steps (b) and (c), and recycling the side-cut liquid as part of the filtrate of the step (d).

TECHNICAL FIELD

The present invention relates to a method for producing polyphenyleneether. More specifically, the present invention relates to a method forproducing the polyether that includes recycle use of a solvent.

PRIOR ART

As a method for synthesizing the polyphenylene ether, there is a methodof subjecting phenol to oxidative polymerization in the presence of acopper compound and amines such as di-n-buthylamine and the like, in anaromatic compound solvent. A non-solvent for the polyphenylene ethersuch as methanol, water or the like is added in the above-obtainedpolyphenylene ether solution to precipitate the polyphenylene etherparticles. Then, dry particles of the polyphenylene ether can beprepared through steps such as solid-liquid separation, washing withmethanol or the like and dryness.

It surely needs to achieve reduction of the manufacture cost thatcomponents used in the above method of preparing the polyphenyleneether, such as the aromatic compound solvent, the amines, methanol orwater, are each separated and recovered for every component to reuse.However when di-n-buthylamine is used especially as the amines, it hasnot been established a method of separating and recovering an aromaticcompound solvent, di-n-buthylamine and methanol efficiently andeconomically.

The present invention has been made to solve the above problems, and theobject of the present invention is to provide an industriallyadvantageous method for producing the polyphenylene ether by separatingand recovering efficiently the solvent used in polyphenylene etherproduction process, such as aromatic compound solvent, amines andmethanol.

Other purposes and advantages of the present invention will become clearfrom the following explanation.

DISCLOSURE OF INVENTION

The present inventors have made extensive studies to solve the aboveproblems, and as a result, have found that it was able to recoveredmethanol having the low amines content and water by adding water to amixed solution of the aromatic compound solvent, amines and methanol,separating a phase which consists of the aromatic compound solvent and alarge portion of the amines from the mixed solution by liquid-liquidseparation, supplying a phase which consists mainly of methanolcontaining a part of the amines and water to a distillation column, anddistilling the phase while carrying out side-cut of the amines. Thus,the present invention has been accomplished.

That is, the present invention is a method for preparing polyphenyleneether comprising the following steps,

(a) a step for synthesizing polyphenylene ether by subjecting phenol tooxidative polymerization in the presence of a copper compound and aminesin an aromatic compound solvent,

(b) a step for precipitating the polyphenylene ether particles by addingmethanol to the solution of polyphenylene ether in the aromatic compoundsolvent obtained by the step (a),

(c) a step for solid-liquid separating a slurry of polyphenylene etherobtained by the step (b), and washing the separated polyphenylene etherparticles with methanol to obtain the polyphenylene ether,

(d) a step for adding water to a filtrate obtained by the step (c) tomix them, and then, liquid-liquid separating the mixture into phaseconsisting mainly of the aromatic compound and a phase consisting mainlyof methanol and water, and

(e) a step for supplying the phase consisting mainly of methanol andwater, obtained by the step (d), to the middle portion of thedistillation column to perform distillation, and separating out adistillate liquid consisting mainly of methanol, a bottom liquidconsisting mainly of water and a side-cut liquid comprising the aminesby distilling, recycling the distillate liquid consisting mainly ofmethanol as methanol which is used at the step (b) and (c), andrecycling the side-cut liquid as part of the filtrate which is used atthe step (d).

EMBODIMENT FOR PRACTICING THE INVENTION

The polyphenylene ether in the present invention is derived from acompound represented by the following formula (1) by oxidativepolymerization.

(wherein R₁, R₂, R₃ and R₄ represent independently a substituentselected from the group consisting of a hydrogen atom, an alkyl group, asubstituted alkyl group, a halogen atom, an aryl group and a substitutedaryl group.)

Examples of polyphenylene ether according to the present invention are ahomopolymer such as

poly(2,6-dimethyl-1,4-phenylene)ether,

poly(2-methyl-6-ethyl-1,4-phenylene)ether,

poly(2,6-diethyl-1,4-phenylene)ether,

poly(2-ethyl-6-n-propyl-1,4-phenylene)ether,

poly(2-methyl-6-n-propyl-1,4-phenylene)ether,

poly(2-ethyl-6-isopropyl-1,4-phenylene)ether,

poly(2-methyl-6-chloroethyl-1,4-phenylene)ether,

poly(2-methyl-6-hydroxyethyl-1,4-phenylene)ether;

polyphenylene ether copolymer such as 2,6-dimethylphenol copolymerizedwith 2,3,6-trimethylphenol and/or o-cresol.

The step (a) of the present invention is a step for obtaining thepolyphenylene ether by subjecting phenol to oxidative polymerization inthe presence of the copper compound and the amines in the aromatichydrocarbon solvent.

The aromatic hydrocarbon solvent used in the reaction of polymerizationis preferably benzene, toluene and xylene, and especially toluene ispreferred. The concentration of polyphenylene ether in a solution ofpolymerization reaction is preferably 5 to 70 wt %, more preferably 10to 50 wt %. Further, the solution may contain substances for removingcatalysts, by-products or the like, other than polyphenylene ether andcatalysts for polymerization (the copper compound and the amines).

The step (b) is a step for precipitating the polyphenylene etherparticles by adding methanol which is a non-solvent for polyphenyleneether, to the solution of polyphenylene ether in the aromatic compoundsolvent, obtained by the step (a).

The amount of methanol to be added is preferable 1 to 2 times by weightof the aromatic compound in polyphenylene ether solution. It isdesirable further to let water co-exist with a mixture of the aromaticcompound solvent and methanol within such a range that the mixture canmaintain a single liquid phase. Moreover, when the solution ofpolymerization reaction is supplied, it is preferred that thepolyphenylene ether solution and methanol are continuously supplied intoone or more stages of a stirring vessel having a reciprocating stirrer.Further, to decrease the amount of methanol used, it is desirable tosupply the polyphenylene ether solution into the stirring vessel whilemaintaining temperature to the extent that polyphenylene ether does notprecipitate after heating and condensing the polyphenylene ethersolution.

The step (c) is a step for solid-liquid separating the slurry ofpolyphenylene ether obtained by the step (b), and then, washing theseparated polyphenylene ethers particles with methanol.

As a method of solid-liquid separating the slurry of the polyphenyleneether particles precipitated, for example, there are a method of using acentrifugal force and a vacuum filtration method under reduced pressure.Moreover, not only these but any method scan be used. The solid-liquidseparated wet particles of polyphenylene ether were washed withmethanol, and dried by heating or the like, to obtain dry particles.Since it is hard to remove the aromatic compound solvent and the aminesby drying, if these are not removed from the wet particles bymethanol-washing, these will remain in the dry particles and will becomecause a stench or the like.

The step (d) is a step for adding water to the filtrate obtained by thestep (c), i.e. the filtrate containing the aromatic compound, the aminesand methanol, and liquid-liquid separating into a phase consistingmainly of the aromatic compound and a phase consisting mainly ofmethanol and water.

It is desirable to set up the amount of water to be added so that theweight ratio of water/methanol in the liquid-liquid separated rawsolution may be 0.5 to 1.5. Further, as for a method of liquid-liquidseparation, there are a stand separation, a centrifugation and a towersystem separation or the like. Moreover, not only these but any methodscan be used. After most of the aromatic compound and the amines arerecovered as the phase consisting mainly of the aromatic compound, ifdesired, it is fractionated to recycle in a polymerization reactionprocess.

The step (e) is a step for supplying the phase consisting mainly ofmethanol and water, obtained by the step (d), i.e. the phase consistingmainly of methanol containing amines, and water to the middle portion ofthe distillation column, and separating out the distillate liquidconsisting mainly of methanol, the bottom liquid mainly consisting ofwater and the side-cut liquid containing the amines. The phaseconsisting mainly of methanol and water, to be distilled preferablycontains 40 to 60 wt % of methanol, 40 to 60 wt % of water and 0.1 to0.3 wt % of the amines.

Though both a tray type column and a packed column can be used as thedistillation column, the tray type column is desirable because of easeof a side-cut. Moreover, there is no particular restriction indistillation pressure.

The distillate solution consisting mainly of methanol, obtained bydistillation is recycled to be used as the non-solvent for precipitatingpolyphenylene ether in the step (b) or as the liquid for washing the wetparticles of polyphenylene ether in the step (c). If the amines inmethanol used as the liquid for washing in the step (c) are contained ina high percentage, it will become inadequate to remove the amines in thepolyphenylene ether particles. Therefore, it is preferable that theconcentration of the amines in the distillate methanol is less than 0.1wt %.

The bottom liquid consisting mainly of water is recycled as water usedin the step (d). To remove the accumulated impurities, it is preferableto discharge at least part of water out of the system. In this case, itis the simplest way to discharge water as drainage, however, when watercontains a high percentage of the amines which becomes a source of CODin drainage, drainage disposal will be complicated. Moreover, since thecost increases due to the supplement of the discharged water, it ispreferable that the concentration of the amines in the bottom liquid isless than 0.01 wt %.

To maintain the concentration of the amines in the distillate solutionand bottom solution less than a certain concentration in the step (e),the solution containing the amines is extracted from the middle portionof the distillation column as the side-cut liquid. It is desirable toset the position for extracting the side-cut liquid so that theconcentration of the amines in the side-cut liquid becomes as high aspossible. Further, it is desirable to set the extracted amount so thatit is 0.5 to 5 wt.% of the phase consisting mainly of methanol andwater, to be distilled. The side-cut liquid is returned to the step (d).Therefore, the most of the amines distributed to the phase consistingmainly of methanol and water in the step (d) circulates between the step(d) and (e), and as a result, the amines which are discharged as thebottom liquid can be held down in a very little.

For the purpose of effective distilling and the like, an anti-foamingagent or sodium hydroxide can be added into the phase consisting mainlyof methanol and water, to be distilled in the step (e). In this case, toavoid returning the additive to the step (d), it is desirable to carryout side-cut from between the tray supplying a material solution and thetop of the distillation column.

Examples of the amines of the present invention include the aminesmaking an azeotrope with water such as di-n-butylamine,n-buthyldimethylamine and the like.

EXAMPLES

The following examples illustrate the present invention morespecifically, but are in no way to be taken as limiting the invention.

Example 1

Two kilograms of cupric bromide was dissolved in 35 kg ofdi-n-buthylamine and 800 kg of toluene. A solution in which 200 kg of2,6-dimethylphenol was dissolved in 500 kg of toluene was added to thiscatalytic solution. This mixed solution was subjected to polymerizationat 40° C. for 3 hours while supplying oxygen into a reactor. After thereaction stopped, the solution was contacted with water to remove thecatalyst from the reaction solution, and the polymerization reactionsolution of polyphenylene ether was obtained. This polyphenylene ethersolution was mixed while stirring with methanol of 1.5 times by weightof toluene in the solution, to precipitate the polyphenylene etherparticles. Then, the solution was separated by a solid-liquid separator,and a wet solid was washed with methanol of 5 times by weight ofpolyphenylene ether in the wet solid. Water was added to thesolid-liquid separated filtrate so that the weight ratio ofwater/methanol after addition might be 1.0, and the solution wassubjected to stand separation to obtain a phase of toluene and a phaseconsisting mainly of methanol and water. When distillation was perform,while carrying out side-cut, by using this phase consisting mainly ofmethanol and water as a material under conditions shown in Table 1, thedistillate and the bottom liquid having the low concentration ofdi-n-buthylamine was obtained. The result was shown in Table 1.

TABLE 1 FlowRate Composition (wt %) Stages (g/h) ME TL DBA waterSupplied Liquid 20 661 50.1 1.7 0.2 48.0 Distilled Liquid 1 338 95.3 3.40.02 1.3 Bottom Liquid 40 305 0.02 <0.01 <0.01 99.98 Side-cut Liquid 1513 43.2 0.1 9.6 47.1 ME: methanol TL: toluene DBA: di-n-buthylamine

Comparative Example 1

An experiment was carried out under the same conditions as Example 1except that distillation was perform, without carrying out side-cut, byusing the phase consisting mainly of methanol and water as a materialunder conditions shown in Table 2. The concentration of di-n-buthylaminein the distillate liquid and bottom liquid obtained by distillation,increased remarkably as compared with Example 1. In addition, thetemperature of each stage of the distillation column was also unstable.The result was shown in Table 2.

TABLE 2 FlowRate Composition (wt %) Stages (g/h) ME TL DBA waterSupplied Liquid 20 655 50.1 1.7 0.2 48.0 Distillate Liquid 1 335 95.43.1 0.18 1.3 Bottom Liquid 40 320 0.04 <0.01 0.22 99.74 ME: methanol TL:toluene DBA: di-n-buthylamino

According to the present invention, the aromatic compound solvent usedfor the production of polyphenylene ether, the amines making theazeotrope with water, and methanol can be separated and collectedefficiently, and polyphenylene ether having low concentration ofresidual solvent can be produced at lower cost.

What is claimed is:
 1. A method for producing polyphenylene ether, whichcomprises (a) a step for synthesizing polyphenylene ether by subjectingphenol to oxidative polymerization in the presence of a copper compoundand amines in an aromatic compound solvent, (b) a step for precipitatingpolyphenylene ether particles by adding methanol into the solution ofpolyphenylene ether in the aromatic compound solvent obtained by thestep (a), (c) a step for solid-liquid separating a slurry ofpolyphenylene ether obtained by the step (b), and then washing theseparated polyphenylene ether particles with methanol to obtain thepolyphenylene ether, (d) a step for adding water to a filtrate obtainedby the step (c) to mix them, and then liquid-liquid separating themixture into a phase consisting mainly of the aromatic compound and aphase consisting mainly of methanol and water, and (e) a step forsupplying the phase consisting mainly of methanol and water, obtained atthe step (d) to the middle portion of a distilled column to performdistillation, and separating out a distillate liquid consisting mainlyof methanol, a bottom liquid consisting mainly of water and a side-cutliquid containing the amines by distillation, recycling the distillateliquid consisting mainly of methanol as methanol of the steps (b) and(c), and recycling the side-cut liquid as part of the filtrate of thestep (d).
 2. The method of claim 1, wherein the amines are amines whichmake an azeotrope with water.
 3. The method of claim 1, wherein theamount of methanol added at the step (b) is 1 to 2 times by weight ofthe aromatic compound in the solution.
 4. The method of claim 1, whereinwater is added so that the weight ratio of water/methanol in theliquid-liquid separated raw material solution in the step (d) is 0.5 to1.5.
 5. The method of claim 1, wherein the phase consisting mainly ofmethanol and water, to be distilled in the step (e) contains 40 to 60 wt% of methanol, 40 to 60 wt % of water and 0.1 to 0.3 wt % of the amines.6. The method of claim 1, wherein the amount of side-cut liquid is 0.5to 5 wt % based on the phase consisting mainly of methanol and water, tobe distilled.
 7. The method of claim 1, the concentration of the aminesin the distillate solution in the step (e) is less than 0.1 wt % and theconcentration of the amines in the bottom liquid is less than 0.01 wt %.8. The method of claim 1, wherein an anti-foaming agent and/or sodiumhydroxide are/is added to the phase consisting mainly of methanol andwater, to be distilled in the step (e), and carrying out side-cutbetween the stage supplying a raw material and the top of thedistillation column.